What is the relationship between MW output and MVAR output?

The relationship between MW (megawatts, a measure of real power) and MVAR (megavolt-amperes reactive, a measure of reactive power) is critical in power system operations, particularly when considering the operation of synchronous machines like generators. Generators produce real power (MW) to load while also managing reactive power (MVAR) to maintain voltage levels.

When a generator is operated at a higher output of real power (MW), it often operates with a reduced reactive power output (MVAR). This phenomenon is mainly due to the limitations of the generator's capability curve, which shows how much real and reactive power it can provide simultaneously. As MW output increases, particularly near its maximum capacity, there’s generally a tendency for MVAR output to decrease. This is because the generator has to meet the demand for real power, thereby reducing its ability to supply reactive power, which is essential for voltage regulation.

Therefore, the correct choice, which indicates that increasing MW generally decreases MVAR, reflects the operational characteristics of generators and their limits in generating both forms of power effectively in an interconnected system. Understanding this relationship is crucial for dispatchers to ensure system stability and reliability.